The invention is related to the field of disk drive systems, and in particular, to a high-speed interface that transfers user data and servo data from a read channel integrated circuit to another integrated circuit.
A magnetic disk system stores user data in data tracks on the surface of a disk device. The user data is transferred between the disk and the user as follows. A head is positioned over a circular data track and reads the user data from the data track as the disk spins. The head transfers the user data to a pre-amp, and the pre-amp transfers the user data to a read channel integrated circuit. The read channel integrated circuit processes the user data and transfers the user data to a drive control integrated circuit over a high speed bus, such as a Non-Return to Zero (NRZ) bus. The drive control integrated circuit transfers the user data to the user.
The magnetic disk system also stores servo position data in servo sectors on the surface of the disk device. The servo sectors are interspersed along the circular data tracks so that the head periodically encounters the servo sectors as the disk spins. When the heads are positioned over a servo sector, they transfer servo data and not user data. When the heads are positioned over a data sector with user data, they transfer user data and not servo data.
A servo system uses the servo data to position a read/write head over a data track that contains the desired user data. One form of servo position data is coarse-resolution data that identifies the data track that is under the head. Coarse-resolution data has a resolution of one track and does not have the resolution to center the head over the data track. The other form of servo position data is high-resolution data that indicates how far off-center a head is relative to the data track. The servo system uses the coarse-resolution data to position a head near the proper data track and uses the high-resolution data to center the head over the center of that track. The servo system must have the servo position data to effectively store or retrieve user data.
Servo position data is transferred from the disk to the servo system as follows. A read/write head reads the servo position data from the disk device. The read/write head transfers the servo position data through a pre-amp to a read channel integrated circuit. The read channel integrated circuit processes the servo position data and transfers the processed data to a drive control integrated circuit. A processor in the drive control integrated circuit uses the servo position data to direct the servo system to position the head.
One prior system for transferring servo position data from the disk to the processor uses dedicated analog connections to transfer the high-resolution data from the read channel integrated circuit to the drive control integrated circuit. The analog lines require dedicated pins on each integrated circuit that increase the cost of the integrated circuits, and the corresponding cost of the disk drive systems that incorporate the integrated circuits. The course-resolution data is transferred from the read channel integrated circuit to the drive control integrated circuit by lines that transmit a representation of the data pulses in the coarse-resolution servo data field. These lines are sometimes referred to as pulse/polarity lines.
Another prior system for transferring servo position data from the disk to the processor uses the read channel integrated circuit to convert the high-resolution data from analog to digital. This prior system then transfers the high-resolution data over a serial interface between the read channel integrated circuit and the drive control integrated circuit. Although, the course-resolution data is still transferred by the pulse/polarity lines, it could be decoded in the read channel integrated circuit and transferred to the drive control integrated circuit over the serial interface. The serial interface can be slow given the typical baud rate and the increase in the amount of servo position data. Unfortunately, the slow speed of the serial interface may limit the accurate positioning of the head to read or write data. The slow speed of the serial interface also limits the ability of the servo system to follow high-density data tracks that increase drive capacity. In addition, it is undesirable to transfer data over the serial interface while data is being read due to signal to noise issues.
At present, there is a need for a more efficient system to transfer servo position data from the read channel integrated circuit to the drive control integrated circuit. Such a system should transfer the servo position data at high speeds and should eliminate the analog pins on the integrated circuits.
The invention overcomes the above problems by providing a high-speed interface that transfers servo position data from the read channel integrated circuit to the drive control integrated circuit. The high-speed interface eliminates the need for analog pins on the integrated circuits to lower the cost of the system. The high-speed interface also eliminates the use of the serial interface to transfer the servo position data which speeds up the data transfer and leaves the serial interface with more capacity for other communications.
The invention includes methods, systems, and integrated circuits for transferring user data and servo position data in a disk drive system. Examples of servo position data include high-resolution servo position data and coarse-resolution servo position data. A read channel integrated circuit transfers the user data and the high-resolution servo position data to a data bus, such as an NRZ bus. The data bus transfers the user data and the high-resolution servo position data to another integrated circuit, such as a drive control integrated circuit. The other integrated circuit receives the user data and the high-resolution servo position data from the data bus.
The read channel integrated circuit is able to transfer servo data over the data bus when the head is positioned over a servo sector because user data is not being transferred over the data bus during this period. Using the same high-speed data bus that transfers user data to also transfer servo position data represents a distinct advance in the art. Use of this bus to transfer servo position data speeds up the data transfer and eliminates the need for analog pins.
The invention has various embodiments and each of the following limitations is not required in each embodiment. A disk stores the user data and the servo position data. A head reads the user data and the servo position data from the disk and transfers the servo position data to a pre-amp. The pre-amp transfers the user data and the servo position data to a read channel integrated circuit. The read channel integrated circuit demodulates the servo position data and the servo bursts that represent the high-resolution servo position data. The read channel integrated circuit converts the high-resolution servo position data from analog to digital. The read channel integrated circuit separates the digital high-resolution servo position data into servo position data words and stores the data words in a memory.
The read channel integrated circuit multiplexes the user data and the servo position data words and transfers the multiplexed data to the data bus. The data bus transfers the multiplexed data to the other integrated circuit. The servo position data is transferred when the disk drive system is not reading or writing user data. The read channel integrated circuit may also decode the coarse-resolution servo position data and separate it into the servo position words along with the high-resolution servo position data. In this case, the coarse-resolution servo position data is also transferred over the data bus.
The other integrated circuit de-multiplexes the user data and the servo position data words. The other integrated circuit combines the servo position data words into the servo position data and stores the servo position data in memory. The other integrated circuit uses the servo position data to control positioning of a head relative to a disk device. The other integrated circuit also transfers the user data to the user.